Although the invention has broader application, for convenience the description will generally relate to its usage in a photo-processing system, and specifically to the removal, and replacement, of a cathode of an electrolytic silver recovery system thereof.
A silver recovery cell, or cartridge, contains a cathode on which silver is plated during operation, for example during the recovery of silver from a fixer solution in a tank of a photo-processor. When the cathode is fully loaded with silver, it has to be removed from the cell by the user. The cathode may be of the reusable type, in which case the silver is removed and the cleaned cathode is replaced in the cell; the silver being sent to a refiner. However, this operation of removing the silver from a cathode is both messy and inconvenient. This inconvenience is reduced when a disposable cathode is used, in which the cathode is generally made of a low-cost conductive material which can be smelted along with the silver. Typical materials for such a disposable cathode are graphite impregnated plastic, graphite foil laminated to plastic sheet, and plastic sheet painted with conductive ink. For a recovery cell having a disposable cathode, the user simply removes the cathode and replaces it with a fresh one; the used cathode then being sent in its entirety for refining.
U.S. Pat. No. 5,370,781 discloses a disposable cathode for use in an electrolytic cell, in which the action of screwing down a lid of the cell both seals the cell and makes electrical contact with the cathode. When the cathode is full of silver, the lid is unscrewed and the wet cathode is removed either by hand or by means of a tool which grasps holes in the top of a cylindrical wall of the cathode. The cathode is removed from the cell and placed in a bag and sealed for transport to the refiner. The operation of removal, and exchange, of the cathode is still messy and requires some skill on the part of the user to avoid contact between any liquid dripping from the cathode and the user and/or associated equipment.
U.S. Pat. No. 5,203,979 also discloses a disposable cathode, and whilst its large size reduces the frequency of changing, the cell must be drained in order to change the cathode, so that bolts passing through the cathode and the cell wall may be released. Removal of the cylindrical cathode is done either manually or by a tool. This operation is both time consuming and messy, especially bearing in mind that the wet cathode may weigh up to several kilograms.
U.S. Pat. No. 4,834,849 discloses yet another type of disposable cathode construction in which the cathode is in the form of conductive paint on a plastic substrate. Replacement of the cathode requires the cell to be drained of its photographic fixer solution, and although the extent of the manual operation is reduced, pouring of liquid, which may cause spills and drips onto associated equipment, is still involved. This method is, therefore, likewise not suited to operation of the cell in an office-like environment.